Relatively few rookeries fell within CBC plots,
but an index calculated from the available nest counts showed
a shallow, long-term increase (Wilson
et al. 1998). The trend is confirmed by the results
of the most recent BTO rookeries survey, which identified a
40% increase in abundance between 1975 and 1996 (Marchant
& Gregory 1999). This increase probably reflects the
species' considerable adaptability in the face of agricultural
change. BBS indices, which are drawn from sightings during transect
walks and not from the BBS nest counts, suggest possible decrease
in Scotland, Wales and Northern Ireland since around 2000. There
have been no clear trends in breeding productivity since the
1960s.